Method and apparatus of converting a series of data words into modulated signals

ABSTRACT

The present invention relates to method and apparatus of modulating a series of data words into (d,k) constrained sequence in order to record onto a recording medium. The present method generates, for each data word, a number of alternative sequences by combining mutually different digital words with the data word, calculates for each alternative sequence a digital sum value (DSV) and a penalty based on respective consecutive-zeros sections within the sequence and a joining consecutive “zeros” to a previously-selected sequence, and selects one alternative sequence for recording onto a recordable medium based on the calculated DSV and penalties. Owing to the present invention, DC component of sequences to be recorded onto a recording medium is suppressed and stabilization of a reproduction clock is improved through writing more edge information (i.e., “1”s).

BACKGROUND OF THE INVENTION

This application is a Continuation of co-pending application Ser. No.10/323,789, filed on Dec. 20, 2002 is now a U.S. Pat. No. 6,696,994, theentire contents of which are hereby incorporated by reference and forwhich priority is claimed under 35 U.S.C. § 120; and this applicationclaims priority of Application No. 2001-0082844 filed in Korea on Dec.21, 2001 under 35 U.S.C. § 119.

FIELD OF THE INVENTION

The present invention relates to method and apparatus of modulating aseries of data words into (d,k) constrained sequence in order to recordonto a recording medium such as magnetic, magneto-optical, or opticaldisk.

DESCRIPTION OF THE RELATED ART

In general, when data is recorded onto a magnetic, magneto-optical, oroptical medium, the data is modulated into a coded sequence matching therecording medium prior to the recording. However, if the coded sequenceresulting from the modulation contains a direct current (DC) component,a variety of error signals such as tracking errors generated in controlof a servo of the disk drive become prone to variations or jitter aregenerated easily.

The first reason for using said dc-free signals in recording onto amedium is that recording channels are not normally responsive tolow-frequency components. The suppression of low-frequency components inthe signal is also highly advantageous when the signal is read from anoptical record carrier on which the signal is recorded in the track,because then continuous tracking control undisturbed by the recordedsignal is possible.

A good suppression of the low-frequency components leads to improvedtracking with less disturbing audible noise. For this reason it is thusdesirable to make as many efforts to prevent the modulated sequence fromcontaining a direct current component as possible.

In order to prevent the modulated sequence from containing a directcurrent component, control of a DSV (Digital Sum Value) has beenproposed. This well-known method is explained briefly.

FIG. 1 shows a block diagram of a general coding system. The codingsystem includes a generator 10 generating a number of codewordcandidates for each input data word; and a selector 20 selecting acodeword with the smallest DSV among the candidates.

FIG. 2 shows a detailed block diagram of the coding system. As shown inFIG. 2, the generator 10 includes an augmentor 100 and a plurality ofNRZI coders 101 to 116 while the selector 20 includes a plurality ofcodeword memories 201 ₁ to 216 ₁, and a plurality of DSV calculators 202₁ to 216 ₂, and a selecting unit 220.

The augmentor 100 generates for each input word a number of codewordcandidates by combining mutually different digital words with the dataword and then scrambles them individually. The codeword candidates canbe generated simply by placing the mutually different digital words infront, middle, or rear of the input data word. If a 4-bit digital wordis used 16 candidates are generated by the augmentor 100. The NRZIcoders 101 to 116 conduct NRZI pre-coding for the respective codewordcandidates. The binary “zeros” outputted from each coder represent no(magnetic flux or electrical intensity) change, while binary “ones”represent transitions from one direction of recorded flux to theopposite direction.

The codeword candidates from the generator 10 are stored in therespective codeword memories 201 ₁ to 216 ₁. Each of the DSV calculators201 ₂ to 216 ₂ calculates DSV of the codeword candidate stored in acorresponding memory and adds the calculated DSV to a total DSVaccumulated from previously selected successive codewords. Eachfinally-calculated total DSV is applied to the selecting unit 220.

Then, the selecting unit 220 compares the inputted final DSVs each otherfrom the DSV calculators 201 ₂ to 216 ₂ to determine the smallest finalDSV. The codeword candidate associated with the determined final DSV isselected. Consequently, a codeword with the smallest DSV is outputtedfrom the selector 20. This process enables a series of codewords withthe least DC component to be recorded onto a recordable medium.

However, if the number of consecutive “0”s within a codeword and thenumber of linking “0”s between the last “1” of the first codeword andthe first “1” of the second in are not limited in the above modulatingprocess, a codeword with relatively long “0”s may be selected. If such acodeword is chosen frequently, there will be too long an unbroken stringof contiguous “0”s with no interspersed “1”s during reproduction, sothat the clock regenerating phase-locked-loop (PLL) will fall out ofsynchronism, which possibly causes data error or reproduction fail.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a coding systembeing able to limit the number of consecutive “0”s between two “1”s inthe process of generating a number of codeword candidates for each inputdata word and selecting a codeword candidate to suppress DC component.

An apparatus of converting a series of data word into a modulated signalin accordance with the present invention is characterized in that itcomprises a generator generating for each data word a number ofalternative sequences by combining mutually different digital words withthe data word; a first calculator calculating a digital sum value foreach alternative sequence; a second calculator calculating for eachalternative sequence a penalty based on respective consecutive-zerossections; and a selector selecting one alternative sequence forrecording onto a recordable medium based on the calculated digital sumvalues and penalties.

A method of converting a series of data word into a modulated signal inaccordance with the present invention is characterized in that itcomprises the steps of: generating for each data word a number ofalternative sequences by combining mutually different digital words withthe data word; calculating, for each alternative sequence, a digital sumvalue and a penalty based on respective consecutive-zeros sections; andselecting one alternative sequence for recording onto a recordablemedium based on the calculated digital sum values and penalties.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the present invention, illustrate the preferredembodiments of the invention, and together with the description, serveto explain the principles of the present invention, and wherein:

FIG. 1 shows a block diagram of a general coding system;

FIG. 2 shows a detailed block diagram of the general coding system; and

FIG. 3 shows a detailed block diagram of a coding system in accordancewith the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In order that the present invention may be fully understood, a preferredembodiment thereof will now be described with reference to theaccompanying drawings.

FIG. 3 shows a detailed block diagram of a coding system in accordancewith the present invention. The coding system of FIG. 3 is composed of agenerator 10 and a selector 50. The generator 10 is composed of anaugmentor 100 and a plurality of NRZI coders 101 to 116 as in theconventional coding system of FIG. 2. The selector 50 includes aplurality of codeword memories 501 ₁ to 516 ₁, and a plurality of DSVcalculators 501 ₂ to 516 ₂, a plurality of k-penalty calculators 501 ₃to 516 ₃, and a selecting unit 520.

Each of the k-penalty calculators 501 ₃ to 516 ₃ calculates k-penalty ofa codeword candidate in proportion to consecutive “0”s within a codewordand linking “0” runs between two consecutive “1”s of two successivecodewords under a given run length limited codes, generically designatedas (d,k) codes. A (d,k) code means constraints that at least d “zeros”are inserted between successive data “ones”, and no more than k “zeros”are inserted between successive data “ones”.

The selecting unit 520 calculates a total penalty for each codewordcandidate from the final DSV calculated by each DSV calculator andk-penalty calculated by each k-penalty calculator, and then chooses onecodeword candidate with the smallest total penalty among the candidatesfor recording onto a recordable medium. The above processes aredescribed below in detail.

The augmentor 100 of the generator 10 generates for each word a numberof codeword candidates by combining mutually different digital words,(e.g., 16 words of ‘0000’,‘0001’,‘0010’, . . . and ‘1111’) with the dataword and scrambles them individually. The codeword candidates can begenerated simply by placing the mutually different digital words infront, middle, or rear of the input data word. The NRZI coders 101 to116 conduct NRZI pre-coding for the respective codeword candidates asexplained before.

The codeword candidates from the generator 10 are stored in therespective codeword memories 501 ₁ to 516 ₁. Each of the DSV calculators501 ₂ to 516 ₂ calculates DSV of the codeword candidate stored in acorresponding memory and adds the calculated DSV to a total DSVaccumulated from previously-selected successive codewords. Thefinally-calculated total DSVs are respectively applied to the selectingunit 520.

Each of the k-penalty calculators 501 ₃ to 516 ₃ counts respective“0”-runs sections within a codeword candidate stored in thecorresponding memory and further counts runs of consecutive “0”s linkingbetween the last “1” of a previously-chosen codeword by the selectingunit 520 and the first “1” of the concerned codeword candidate. Then,the k-penalty calculator imposes a k-penalty to the concerned candidatein consideration of the respective counts.

That is, the k-penalty calculator compares each count Ki with tworeferences n and m (0<n<m). If Ki is between n and m inclusive, it ismultiplied by a weighting factor Wa, and if Ki is greater than m it ismultiplied by another weighting factor Wb (>Wa). After the Pi (=Ki×(Waor Wb)) is calculated for each consecutive “0”s, it is summed altogetherto obtain total k-penalty Kpen$\left( {= {\sum\limits_{i}\; P_{i}}} \right).$If all of the counts Ki are smaller than n, the k-penalty Kpen is set to0.

For example, if the concerned codeword candidate is “001001000010000001”and the previously-selected codeword is “100100101000001000”, respectivecounts of consecutive-“0”s sections are 5, 2, 4, and 6 in turn.Supposing that Wa=0.3, Wb=0.6, n=3, and m=5, 4 and 5 between n and minclusive are multiplied respectively by Wa=0.3, and the count 6 beyondm is multiplied by Wb=0.6. The respective results are then summed to 6.9(=Kpen=Wa×Ki+Wb×Ki=0.3×(4+5)+0.7×6) that is k-penalty.

A coding system can be designed by a designer who develops a diskrecording device such that the weighting factors Wa and Wb areadjustable.

As another embodiment of k-penalty calculation, the longest consecutive“0”s only may be considered irrespective of other remaining “0” runs.

The selecting unit 520 compares the inputted final DSVs and thek-penalties (Kpen) from the DSV calculators 501 ₂ to 516 ₂ and thek-penalty calculators 501 ₃ to 516 ₃ to select a codeword optimal to DSVcontrol and PLL locking. That is, a codeword satisfying smaller DSV andshorter consecutive “0”s at the same time is selected.

For selecting a codeword among a plurality of candidates inconsideration of DSV and k-penalty, sum of two values can be comparedeach other. In this embodiment, a codeword candidate with the smallestsum of DSV and k-penalty assigned as above is selected for recordingonto a recording medium such as magnetic, magneto-optical, or opticaldisk.

Instead of simple summation of the two values of DSV and k-penalty, thetwo values may be summed after they are multiplied by adequate weightfactors, respectively.

The method and apparatus of converting a series of data words into amodulated signal according to the present invention not only cansuppress DC component of sequences to be recorded onto a recordingmedium but also can improve stabilization of a reproduction clockthrough writing edge information (i.e., “1”) as frequently as it can.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. An apparatus of converting a series of data word into a modulatedsignal, comprising: a generator generating for each data word a numberof alternative sequences by combining mutually different digital wordswith the data word; a first calculator calculating a digital sum valuefor each alternative sequence; a second calculator calculating for eachalternative sequence a penalty based on respective consecutive-zerossections, wherein the longest consecutive zeros are considered tocalculate the penalty; and a selector selecting one alternative sequencefor recording onto a recordable medium based on the calculated digitalsum values and penalties.
 2. The apparatus of claim 1, wherein saidgenerator comprises: an augmentor generating for each data word 2^(N)intermediate sequences by combining the N-bit digital words with thedata word; and a coder conducting NRZI coding for each generatedintermediate sequence to produce the 2^(N) alternative sequences.
 3. Theapparatus of claim 1, wherein said second calculator calculates thepenalty in further consideration of joining consecutive zeros betweeneach alternative sequence and a previously-selected sequence by saidselector.
 4. The apparatus of claim 1, wherein said second calculator,for each alternative sequence, counts respective consecutive-zerossections, compares each count with a reference, multiplies each count bya weighting factor determined from the comparison, and sums themultiplied results altogether to produce said penalty.
 5. The apparatusof claim 1, wherein said selector selects one alternative sequence withthe smaller digital sum value and the shorter penalty among thegenerated plural alternative sequences to record onto a recordablemedium.
 6. A method of converting a series of data word into a modulatedsignal, comprising the steps of: (a) generating for each data word anumber of alternative sequences by combining mutually different digitalwords with the data word; (b) calculating, for each alternativesequence, a digital sum value and a penalty based on respectiveconsecutive-zeros sections, wherein the longest consecutive zeros areconsidered to calculate the penalty; and (c) selecting one alternativesequence as a modulated data based on the calculated digital sum valuesand penalties.
 7. The method of claim 6, wherein said step (a) generatesfor each data word 2^(N) intermediate sequences by combining the N-bitdigital words with the data word, and conducts NRZI coding for eachgenerated intermediate sequence to produce the 2^(N) alternativesequences.
 8. The method of claim 6, wherein said step (b) calculatesthe penalty in further consideration of joining consecutive zerosbetween each alternative sequence and a previously-selected sequence bysaid step (c).
 9. The method of claim 7, wherein said step (b), for eachalternative sequence, counts respective consecutive-zeros sections,compares each count with a reference, multiplies each count by aweighting factor determined from the comparison, and sums the multipliedresults altogether to produce said penalty.
 10. The method of claim 6,wherein said step (c) selects one alternative sequence with the smallerdigital sum value and the shorter penalty among the generated pluralalternative sequences to record onto a recordable medium.
 11. Arecording medium, including at least one sequence that has been recordedthereon through the following steps of: generating for each data word anumber of alternative sequences by combining mutually different digitalwords with the data word; calculating, for each alternative sequence, adigital sum value and a penalty based on respective consecutive-zerossections, wherein the longest consecutive zeros are considered tocalculate the penalty; and selecting one alternative sequence forrecording based on the calculated digital sum values and penalties.